An active galaxy is a star system with a humongous black hole at its centre. 一個活躍的星系是一個中央部位有一個極大的黑洞的恆星體系。
Initially the gas in the cluster is very hot, and the supermassive black hole in a centrally located large galaxy is quiet. 起初星系團里的氣體溫度極高，而位在星系團中央巨大星系裡的黑洞並不活躍。
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